(273g) Modeling of Suspension Flows in Coating Dies

Handling and coating of suspensions is challenging as often the suspended particles agglomerate, marring the functionality of the final product. Practice has shown that such agglomeration can occur as the suspension flows inside the coating die. Modeling of this two-phase flow illuminates how and why agglomeration occurs and how it can be avoided.

The Discrete Element Method (DEM) is used to predict the trajectories of individual particles of a suspension. Forces acting on each particle arise from particle-particle interaction: long-range electrostatic, hydrodynamic, collision, and short-range colloidal forces; particle-wall interaction: hydrodynamic, collision, and short-range colloidal forces; and particle-liquid interaction: drag force. The relative magnitude of these forces determines whether the particles form large coagulations.

To investigate the progress of a large number of particles, the DEM algorithm is modified for parallel execution, following the techniques for parallelization of molecular-dynamic simulations. This enables the tracking of thousands of sub-micron sized particles in life-size coating dies. Emphasis is given on how the suspension behaves as it flows through sharply curved portions of the die; it is usually at such sections that agglomerates and depositions form.